The invention relates to the field of poly- and oligosaccharides and their nutritional effects. In particular, it relates to the application of α-glucanotransferases in methods for preparing dietary fibers, including prebiotic oligosaccharides, and to novel oligosaccharides obtainable thereby.
The term ‘dietary fibre’ was first used in 1953 by Hipsley to describe the plant cell wall components of food. Today there are many definitions of fibre in use, but as yet there is no universally accepted definition. Generally, fibres are derived from carbohydrate sources that have a non-digestible component. Fibres are typically divided into two categories; the insoluble fibres such as wheat bran, resistant starch, hemicelluloses, lignin etc., and the soluble fibres, which can be further classified into two subdivisions: short chain length soluble fibres, including polydextrose, inulin and oligosaccharides, and long chain length soluble fibres including pectins, gums (guar, locust bean, carrageenan, xanthan) and β-glucan (from oat or barley for example).
Prebiotics are dietary fibres, as they are not digested by human enzymes but fermented by the flora of the large intestine. Thus they increase biomass and frequency of defecation, thus having a positive effect on constipation and on the health of the mucosa of the large intestine. Prebiotic carbohydrates are naturally occurring and can be found in numerous foods, including asparagus, chicory, tomatoes and wheat, as well as being a natural component of breast milk.
The term prebiotic was first defined by Gibson and Roberfroid in 1995. However, the initial definition proved difficult to verify and since then the authors have further developed the concept proposing a new definition: “A prebiotic is a selectively fermented ingredient that allows specific changes both in the composition and/or activity in the gastrointestinal microflora that confers benefit upon host well-being and health” (Nutr Res Rev 2004; 17: 259-275). In order to qualify for prebiotic classification, an ingredient is therefore required to (i) resist digestion (gastric acidity, hydrolysis by mammalian enzymes and gastrointestinal absorption); (ii) be fermented by the gastrointestinal microbiota; and (iii) selectively stimulate the growth and/or activity of intestinal bacteria associated with health and well-being. The latter criterion is the main distinguishing feature between a dietary fibre and a prebiotic. Prebiotics are generally recognised for their ability to alter the colonic microbiota, promoting a healthier composition and/or activity by increasing the prevalence of saccharolytic (carbohydrate fermenting) micro-organisms while reducing putrefactive (protein fermenting) micro-organisms.
Established non-digestible carbohydrates that fulfil the prebiotic criteria include fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), lactulose, inulin and polydextrose.
Polydextrose is a polysaccharide composed of randomly cross-linked glucose units with all types of glycosidic bonding. Litesse polydextrose is resistant to digestion due to its unique arrangement of glycosidic linkages. Molecularly, (α1→6) bonds predominate, but about 13% of the polymer has (α1→4) linkages, which can be hydrolyzed by enzymes in the human small intestine. It is fermented throughout the colon and is particularly efficient at mediating a prebiotic effect in the distal colon. Human intervention studies have demonstrated that Litesse polydextrose enhances both bifidobacteria and lactobacilli in a dose dependent manner.
Starch is a polysaccharide found commonly in green plants—those containing chlorophyll—as a means of storing energy. Starch forms an integral part of the multi-billion food ingredients market and is characterised by its complex and consolidated nature. Starch is an ideal example of an essential commodity with a wide array of industrial applications, which include paper and card-board making, fermentation, biofuels, biodegradable plastics and detergents, bio-pesticides, surfactants, polyurethane, resins, binders and solvents. However, it is the food industry that provides the largest market for starch and its derivatives.
Starch is either degraded completely in the small intestine to glucose and taken up in the blood or those parts that escape digestion end up in the large intestine where they serve as a general substrate for the colonic microbial flora. Starch and its derivatives in itself do not stimulate specific beneficial colon microbes. Thus, starch in itself is not a prebiotic compound. The partial solution to the problem is to degrade starch into the disaccharide maltose and then use a transglucosidase enzyme to convert the maltose into (α1→6)-linked isomalto-oligosaccharides (IMO) with a degree of polymerization of 2 to 4. These IMO products are, however, too short and are mostly degraded in the small intestine, thus not reaching the colon. That part of the IMO product that reaches the colon is quickly degraded in the proximal part of the colon by the intestinal microflora and does not reach the distal part were more malign, protein degrading bacteria reside. To outcompete these malign bacteria by stimulating beneficial bacterial species, in particular bifidobacteria, longer isomalto-oligosaccharides are required.
Previously, various methods have been developed for chemical modification of malto-oligosaccharides (MOS) and starch (amylose, amylopectin). More recently, also various transglycosylase enzymes (cyclodextrin glucanotransferase, amylomaltase, starch branching enzyme) have been used for modification of starch (amylose, amylopectin).